Light emitting device and method of manufacturing the same, and display device

ABSTRACT

A light emitting device includes a light emitting element, a light-transmissive member covering the light emitting element, a fluorescent material contained in the light-transmissive member, and a multilayer film disposed on the light-transmissive member and including alternatively layered two types of films of different refractive indices, in which the two types of films are aggregated nano-particles of TiO 2  and aggregated nano-particles of SiO 2 .

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This is a divisional application of U.S. patent application Ser. No.15/649,149, filed Jul. 13, 2017, which claims priority under 35 U. S. C.§ 119 to Japanese Patent Application No. 2016-138417, filed Jul. 13,2016. The contents of this application are incorporated herein byreference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a light emitting device, a method ofmanufacturing the light emitting device and a display device.

Description of Related Art

Generally, a light emitting device has a light emitting element such asa light emitting diode (LED) and a light-transmissive resin covering thelight emitting element, and further, a fluorescent material to convertwavelength of light from the light emitting element is added in thelight-transmissive resin. Light from the fluorescent material and lightfrom the light emitting element are extracted from the light emittingdevice and mixed light is emitted from the light emitting device.Accordingly, the color of light emitted from the light emitting deviceis dependent on the colors and emission intensity of light emitted fromthe light emitting element and the fluorescent material. Therefore, whenthe emission wavelength of the light emitting element and the amount ofthe fluorescent material used in the light emitting device have a largeshift from respective predetermined values, the resulting color of lightextracted from the light emitting device may not meet the requirements.

A light emitting device capable of adjusting emission color is describedin Japanese Unexamined Patent Application Publication No. 2015-026698.

Also, a semiconductor light emitting element having an optical filter ata light extraction side of the wavelength converting layer that includesa fluorescent material is described in Japanese Unexamined PatentApplication Publication No. 2011-198800.

Also, an LED light emitting device having an LED element to emitultraviolet light, a light-transmissive sealing member containingfluorescent material particles and sealing an upper surface of the LEDelement, and a dielectric multilayer film to reflect ultraviolet lightonto an upper surface of the light-transmissive sealing member isdescribed in Japanese Unexamined Patent Application Publication No.2014-222705.

SUMMARY

A light emitting device according to certain embodiments of the presentdisclosure includes a light emitting element, a light-transmissivemember covering the light emitting element and configured to allow lightfrom the light emitting element to pass through, a fluorescent materialcontained in the light-transmissive member to convert wavelength oflight from the light emitting element, and a multilayer film in whichtwo or more types of films of aggregated nano-particles are layered, themultilayer film including a first film of aggregated firstnano-particles and a second film of aggregated second nano-particlesthat has a refractive index different from a refractive index of thefirst nano-particles.

A method of manufacturing a light emitting device according to certainembodiments of the present disclosure includes; providing a lightemitting device, the light emitting device including a light emittingelement covered by a light-transmissive member that is configured toallow light from the light emitting element to pass through, and afluorescent material to convert wavelength of light from the lightemitting element, the fluorescent material being contained in thelight-transmissive member; and disposing a multilayer film on thelight-transmissive member. The step of disposing the multilayerincludes, applying a first slurry comprising first nano-particlesdispersed in a first solvent on the light-transmissive member to disposea first film of aggregated first nano-particles; applying a secondslurry comprising second nano-particles dispersed in a second solvent onthe first film to dispose a second film, the second nano-particleshaving a refractive index different from a refractive index of the firstnano-particles; and repeating the disposing of the first film and thesecond film to dispose a multilayer film having a predetermined numberof layered films.

A light emitting device according to other certain embodiments of thepresent disclosure includes a light emitting element, alight-transmissive member allowing light from the light emitting elementto pass through, a fluorescent material contained in thelight-transmissive member to convert wavelength of light from the lightemitting element, and a multilayer film disposed on thelight-transmissive member. When the peak wavelength of light emittedfrom the light emitting element is indicated as λ, at least one film inthe multilayer film satisfies n₁·d₁=(2N−1)/4·λ (where d₁ is thethickness of the film, n₁ is the refractive index at the peakwavelength, and N is a natural number), and at least one film in themultilayer film satisfies n₂·d₂=(2N−1)/4·λ (where d₂ is the thickness ofthe film, n₂ is the refractive index at the peak wavelength, and N is anatural number which is n₂≠n₁). A light emitting device according toother certain embodiments of the present disclosure includes at leastone film in the multilayer film satisfying, when the peak wavelength oflight emitted from the light emitting element is indicated as λ′,n₁′·d₁′=N/2·λ′ (where d₁′ is the thickness of the film, n₁′ is therefractive index at the peak wavelength, and N is a natural number), andat least one film in the multilayer film satisfying n₂′·d₂′=N/2·λ′(where d₂′ is the thickness of the film, n₂′ is the refractive index atthe peak wavelength, and N is a natural number which is n₂′≠n₁′).

A display device according to certain embodiments of the presentdisclosure includes a lighting device having the light emitting device,and a display panel provided with a color filter having a plurality ofcolor portions at least including portions having a blue color, a greencolor, and a red color, and configured to display an image by usinglight from the lighting device.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is a cross-sectional view schematically showing a configurationof a light emitting device according to one embodiment.

FIG. 2 is a partial cross-sectional view schematically showing aconfiguration of a multilayer film of the light emitting deviceaccording to one embodiment.

FIG. 3 is a schematic partial cross-sectional view of the light emittingdevice, schematically illustrating operation of the light emittingdevice according to one embodiment.

FIG. 4 is a schematic diagram showing matching between the emissionspectrum of the light emitting device according to one embodiment andtransmission spectra of three different color filters.

FIG. 5 shows chromaticity coordinates of light from the light emittingdevice according to one embodiment and light from the light emittingelement and the fluorescent material in the light emitting devicetransmitted through the color filter.

FIG. 6 is a flow chart showing a flow of a method of manufacturing alight emitting device according to one embodiment.

FIG. 7 is a diagram showing a simulation result of a reflection spectrumof five-layer film of TiO₂/SiO₂, and an emission spectrum of light fromthe light emitting element and the fluorescent material of the lightemitting device.

FIG. 8 is a diagram showing ratios of the emission intensities of thelight emitting device after disposing a three-layer film or a five-layerfilm to before disposing respective layered film, in which films ofaggregated TiO₂ nano-particles and aggregated SiO₂ nano-particles arealternately layered.

DETAILED DESCRIPTION

In the following, certain embodiments will be described with referenceto the drawings. The embodiments shown below are intended asillustrative of a light emitting device to give a concrete form totechnical ideas of the present invention, and the scope of the presentinvention is not limited to those described below. Further, the size,material, shape, relative arrangement and the like of constituentcomponents described in the embodiments are not intended to limit thescope of the present invention thereto unless otherwise specified, andthey are given as examples. Note that the sizes and the arrangementrelationships of the members in each of drawings are occasionally shownexaggerated and shapes may be simplified for ease of explanation.

Light Emitting Device

A light emitting device according to one embodiment will be describedwith reference to FIG. 1 and FIG. 2. FIG. 1 is a cross-sectional viewschematically showing a configuration of the light emitting deviceaccording to one embodiment. FIG. 2 is a partial cross-sectional viewschematically showing a configuration of a multilayer film of the lightemitting device according to one embodiment. The shapes and particlesizes of the nano-particles 71 a and 72 a and the number of layers ofthe nano-particles per single layer of the high refractive index layer71 and the low refractive index layer 72 shown in FIG. 2 are given as anexample.

The light emitting device 10 includes a light emitting element 1, alight-transmissive member 5 covering the light emitting element 1 andconfigured to allow light from the light emitting element 1 to passthrough, a fluorescent material 6 contained in the light-transmissivemember 5 to convert wavelength of light from the light emitting element1, and a multilayer film 7. In the multilayer film 7, two or more typesof films of aggregated nano-particles are layered, the films include ahigh refractive index layer 71 of aggregated first nano-particles 71 aand a low refractive index layer 72 of aggregated second nano-particles72 a having a refractive index different from the refractive index ofthe first nano-particles 71 a. The light emitting device 10 furtherincludes a light-reflecting member 2, leads 3 a and 3 c, and wires 4. InFIG. 1, the light-transmissive member 5 is assumed to be transparent andis depicted without hatching etc. The light emitting device 10 alsoincludes a light-reflecting member 2 that defines a recess provided withan opening, and is configured to emit white light of predetermined colorin an upward direction from the opening of the recess. In the presentspecification, the terms such as “upper” and “lower” are used in thesame way as shown in FIG. 1, unless otherwise specified.

Light Emitting Element

The light emitting element 1 serves as a light source in the lightemitting device 10, and a single light emitting element 1 is housed inthe recess formed with an upward opening in the light-reflecting member2, and is placed on a lead 3 a provided as a part of a bottom surface ofthe recess. In the present embodiment, the light emitting element 1 is aface-up mounting type, having n-side and p-side electrodes on its uppersurface, and the electrodes are electrically connected to the leads 3 aand 3 c via wires 4, respectively.

The light emitting element 1 is, for example, a light emitting diode(LED) configured to emit light of an appropriate wavelength, and a lightemitting element 1 that is configured to emit blue light (wavelength ina range of 430 nm to 475 nm) is preferably used. For such an LED, forexample, a nitride-based semiconductor In_(X)Al_(Y)Ga_(1-X-Y)N, (0≤X,0≤Y, X+Y<1) can be used. In the present embodiment, the light emittingelement 1 is designed to emit blue light with a peak wavelength λ₀ of450 nm, which may produce light having a peak wavelength λ equal to thedesigned value λ₀ or a value near λ₀. The light emitting element 1 canhave appropriate shape and size according to purpose.

Light-Reflecting Member

The light-reflecting member 2 is an exterior of the light emittingdevice 10, and also serves as a base to support the light emittingelement 1 and the leads 3 a and 3 c, and as a light-reflector used toefficiently emit light upward. Further, in the manufacturing of thelight emitting device 10, the light-reflecting member 2 also serves as adam at the time of disposing the light-reflecting member 5 and themultilayer film 7. The light-reflecting member 2 has an external shapeof an approximately rectangular parallelepiped elongated along analignment of the leads 3 a and 3 c, and defines a recess with an upwardopening. In addition to the above, the light-reflecting member 2 may beprovided with a marking recess for identifying polarity in the lightemitting device 10. The recess in the light-reflecting member 2 isformed with a size that can house the light-reflecting member 1 andallows wire bonding of the wires 4, and four lateral surfaces definingthe recess are tapered widening upward to reflect light mainly to theupward direction. The light-reflecting member 2 and the leads 3 a and 3c are together constitute the package 20, in which the light-reflectingmember 2 holds the leads 3 a and 3 c such that each of the leads 3 a and3 b serves as a part of the bottom surface of the recess and alsopenetrates the light-reflecting member 2 to the outside.

The light-reflecting member 2 is made of an insulating material havingstrength (hardness) sufficient to serve as the base and allowing to beformed in the shape as described above. More specifically, the sealingmember 2 can be formed with a base material of resin such as siliconeresin, modified silicone resin, epoxy resin, modified epoxy resin,acrylic resin, or a hybrid resin containing one or more of those resins,and a light-reflecting material added to the base material. Examples ofthe light-reflecting material include oxides of Ti, Zr, Nb, Al, and Si,and AlN, MgF₂, and BN, of those, titanium oxide (TiO₂) is preferable.

Lead

The leads 3 a and 3 c are wirings to supply electric current from theoutside of the light emitting device 10 to the light emitting element 1.The lead 3 a serves as a positive electrode and is electricallyconnected to the p-side electrode of the light emitting element 1 via awire 4. The lead 3 c serves as a negative electrode and is electricallyconnected to the n-side electrode of the light emitting element 1 viaanother wire 4. The leads 3 a and 3 c each has a substantiallyflat-plate shape and held by the light-reflecting member 2 so that thesubstantially flat surface of the leads 3 a and 3 b are substantially inparallel to the upper surface of the light emitting device 10. In moredetail, the leads 3 a and 3 c are arranged in a longitudinal directionof the light-reflecting member 2, spaced from each other on the bottomsurface of the recess of the light-reflecting member 2 so that portionsof the leads 3 a and 3 c penetrate through and are protruded outsidefrom the light-reflecting member 2, respectively. The lead 3 a isarranged longer than the lead 3 c at the bottom surface of the recess sothat the light emitting element 1 can be placed on the lead 3 a. Theregion on the bottom surface of the recess of the light-reflectingmember 2 where the leads 3 a and 3 c are arranged is indicated as aninner lead portion which is used as a wire bonding region and alsoconstitutes a light-reflecting surface. The portions of the leads 3 aand 3 c that are protruded outside of the light-reflecting member 2 areindicated as outer-lead portions and are electrically connected to thewirings or the like located outside of the light emitting device 10. InFIG. 1, the outer lead portions of the light emitting device 10 haveplate-like shapes and continuous to the inner lead portions, but forexample, the outer lead portions may be bent downward along thelight-reflecting member 2. The leads 3 a and 3 c are preferably made ofa metal plate of Cu, a Cu alloy, or the like, and further, Ag plating orthe like may be applied at least on the upper surfaces of the inner leadportions to obtain good light-reflecting surfaces.

Wire

Wires 4 are electrically conductive wires used to electrically connectthe p-side and the n-side electrodes of the light emitting element 1with the inner lead portions of the leads 3 a and 3 c, and morespecifically, are wires for wire bonding, which are, for example, Auwires.

Light Transmissive Member

The light-transmissive member 5 serves as a sealing member, disposed inthe recess of the light-transmissive member 2 to enclose the lightemitting element 1 and the wires 4, so as to protect them from externalenvironment. The light-transmissive member 5 also serves as a base fordisposing the fluorescent material 6. The light-transmissive member 5 ismade of an insulating and light-transmissive material, and athermosetting resin, for example, silicone resin, epoxy resin, or urearesin may be used.

Fluorescent Material

The fluorescent material 6 is dispersed in the light-transmissive member5 and can be excited by blue light emitted from the light emittingelement 1 and each component of the fluorescent material 6 emits lightof a specific wavelength. It is preferable that the fluorescent material6 can convert light to green light, yellow light, or red light. In orderto obtain light of a desired color in combination with blue light, thelight emitting device 10 employs one type or two or more types offluorescent materials. In the present embodiment, two types offluorescent materials 61 and 62 are employed as the fluorescent material6. The fluorescent materials 61 and 62 can be excited by blue lightemitted by the light emitting element 1, and to emit light; thefluorescent material 61 emits green light (peak wavelength of 540 nm)and the fluorescent material 62 emits red light (peak wavelength 630nm).

The ratio of the fluorescent materials 61 and 62 and the content, thestate of dispersion, and so forth of the fluorescent materials 61 and 62in the light-transmissive member 5 are designed in combination with thestructure of the multilayer film 7 so that the light extracted from thelight emitting device 10 has a desired color and light quantity(intensity). The fluorescent materials 61 and 62 are approximatelyuniformly dispersed in the light-transmissive member 5, but for example,the fluorescent materials 61 and 62 may be dispersed in thelight-transmissive member 5 more densely near the light emitting element1.

Multilayer Film

The multilayer film 7 is disposed on the light-transmissive member 5, inother words, the multilayer film 7 is disposed at the light emittingside of the light emitting device 10, so that a portion of light passedthrough the light-transmissive member 5 is directed upward to theoutside of the light emitting device 10 and other portion of the lightis reflected downward to return to the light-transmissive member 5. Inthe light emitting device 10, the multilayer film 7 is, together withthe light-transmissive member 5, provided in the recess of thelight-reflecting member 2 and covers an entire of the upper surface ofthe light-transmissive member 5. The multilayer film 7 serves as adistributed Bragg reflector (DBR) film that selectively and stronglyreflect blue light, so that wavelength conversion efficiency of thefluorescent materials 61 and 62 contained in the light-transmissivemember 5 can be enhanced.

The multilayer film 7 includes two or more layers of two or more typesof films of different refractive indices. When two types of films areemployed, the two types of films are alternatively layered, and whenthree or more types of films are employed, films are layered so thatfilms of the same type or same refractive index are not successivelylayered. In the present embodiment, the multilayer film 7 is made of twotypes of films: a high refractive index layer 71 and a low refractiveindex layer 72, that are alternatively layered, and includes five layersof films 71, 72, 71, 72, and 71 that are successively layered from thebottom at the light-transmissive member 5 side. In the multilayer film7, the terms “high refractive index” and “low refractive index” used inthe high refractive index layer 71 and the low refractive index layer 72are used as relative terms. In the present specification, the term“refractive index” is a value at the peak wavelength λ of light emittedfrom the light emitting element 1, unless otherwise specified.

The multilayer film 7 exhibits higher reflectance with greater number ofrepetition of layering the high refractive index layers 71 and the lowrefractive index layers 72, that is, greater number of pairs. Further,to some degree, the greater the number of layers in the multilayer film7, the easier to adjust each reflectance in two or more desiredwavelength regions, as described below. Meanwhile, the greater thenumber of the layers in the multilayer film 7, the greater thethickness, which may increase attenuation of light, which may decreasethe light extraction efficiency of the light emitting device 10. Thenumber of pairs in the multilayer film 7 is determined mainly based onthe refractive indices n₁ and n₂ of the high refractive index layer 71and the low refractive index layer 72 or the like to obtain a desiredvalue of the reflectance for the blue light emitted from the lightemitting element 1. Further, the multilayer film 7 has a high refractiveindex layer 71 as its uppermost layer, which increases the difference inthe refractive indices between the ambient air and the light emittingdevice 10 and thus increases the reflectance of the light at the uppersurface of the multilayer film 7. In the light emitting device 10, thehigh refractive index layer 71 has a refractive index that issufficiently different from that of the light-transmissive member 5.

The high refractive index layer 71 and the low refractive index layer 72that constitute the multilayer film 7 are films of aggregatednano-particles 71 a and 72 a, respectively. In the presentspecification, the term “nano-particles” refers to particles withparticle size in a range of 1 nm to 100 nm. The particle size of thenano-particles 71 a and 72 b can be measured by using a dynamic lightscattering method, a diffusion method, a diffraction method, or thelike. Also, a “film of aggregated nano-particles” may be formed bydispersing primary particles of a particle material in a solvent toobtain a slurry and applying the slurry on a component to be coated withthe particles, and allowing the primary particles to aggregate in thecoating film, as described below. In some cases, secondary particles tobe described below may also be mixed in the slurry as well as theprimary particles. Further, the term “nano-particles” in the “film ofaggregated nano-particles” refers to primary particles or secondaryparticles formed by densely aggregating plurality of primary particles(aggregated particles) or both the primary particles and the secondaryparticles. Accordingly, the primary particles preferably have smallersize than the secondary particles that are the nano-particles 71 a and72 a in the high refractive index layer 71 and the low refractive indexlayer 72. The particle size of the primary particles can be measured byusing a microscopic observation method, a BET method, or the like. Theparticle size of the primary particles can be determined as an averagevalue or a mean value and preferably 50 nm or less. The smaller theparticle size the higher transparency of the high refractive index layer71 and the low refractive index layer 72, which allows a decrease inattenuation of propagating light. The primary particles of the particlesize 5 nm or greater is preferable in practical use.

In a film of aggregated nano-particles, the closer the volume ratio ofthe nano-particles in the film (filling rate) to 100%, the closer theproperties such as a refractive index to that of the primary particles.In a film of aggregated nano-particles, gaps may present between thenano-particles and substances, for example, resin used as a binder, air,and/or a slight amount of dispersion agent added in the slurry, may beincluded in the gaps between the nano-particles, and the smaller thefilling rate of the nano-particles, the greater the properties of thosesubstances affect. The high refractive index layer 71 preferably containthe nano-particles 71 a at a filling rate of 50% or greater, and theresin, air, or the like, described above may also be included in thegaps. For the resin, those exemplified for the light-transmissive member5 can also be used. Similarly, the low refractive index layer 72preferably contain the nano-particles 72 a at a filling rate of 50% orgreater, and the resin, air, or the like, described above may also beincluded in the gaps between the nano-particles 72 a, and particularly,when air is included, the refractive index can be reduced. For example,when gaps including air present in the low refractive index layer 72,the filling rate of the nano-particles 72 a in the high refractive indexlayer 71 disposed on the low refractive index layer 72 is preferablyhigh to a degree so that the primary particles in the slurry do notenter the gaps. In the film of aggregated nano-particles, the fillingrate of the nano-particles may be obtained by, for example, measuringthe film thickness and calculating from the content of the slurry andthe coating amount per unit area. The particle sizes and the fillingrates of the nano-particles 71 a and 72 a in the high refractive indexlayer 71 and the low refractive index layer 72 can be adjusted by theparticle sizes of the primary particles, content of the respectiveslurry, and the like.

In order to increase the reflectance of light at the multilayer film 7,two films that in contact with each other, namely, the high refractiveindex layer 71 and the low refractive index layer 72 preferably have asufficient degree of difference in the refractive indices at the peakwavelength λ of light emitted from the light emitting element.Alternatively, the first nano-particles 71 a and the secondnano-particles 72 a have a sufficient degree of difference in therefractive indices at the peak wavelength λ of light emitted from thelight emitting element. More specifically, the difference in therefractive indices is preferably 0.05 or greater, more preferably 0.1 orgreater, further preferably 0.2 or greater. The greater the difference,the higher the reflectance at the multilayer film 7. In order to obtainthe high refractive index layer 71 and the low refractive index layer 72as described above, two different types of the materials that have asufficient difference in the refractive indices may be selected fromoxides, fluoride, nitrides of metals for the nano-particles 71 a and 72a. For example, for the nano-particles 71 a of the high refractive indexlayer 71, titanium oxide (TiO₂), zinc oxide (ZnO), zirconia (ZrO₂),alumina (Al₂O₃) etc., for the nano-particles 72 a of the low refractiveindex layer 72, silica (SiO₂), magnesium fluoride (MgF₂) etc., may beused. In the present embodiment, TiO₂ for the nano-particles 71 a andSiO₂ for the nano-particles 72 a are respectively employed. As describedabove, the refractive indices n₁ and n₂ of the high refractive indexlayer 71 and the low refractive index layer 72 are affected not only bythe refractive indices of TiO₂ and SiO₂, which are the materials of thenano-particles 71 a and 72 a, but also by the filling rate etc.Therefore, it is preferable to measure the refractive indices n₁ and n₂of samples of the high refractive index layer 71 and the low refractiveindex layer 72 to obtain desired conditions.

The multilayer film 7 is configured to selectively and strongly reflectblue light emitted by the light emitting element 1. To achieve theabove, the high refractive index layer 71 and the low refractive indexlayer 72 are designed in consideration of the film thicknesses d₁ and d₂with the refractive indices n₁ and n₂, respectively. For example, whenthe formulas (1) and (2) are satisfied, a maximum intensity of thereflected light having a wavelength λ can be obtained. The filmthicknesses d₁ and d₂ of the high refractive index layer 71 and the lowrefractive index layer 72 can be measured by observing a cross sectionof each layer with an electron microscope. In the formulas (1) and (2)shown below, “N” is a natural number which may differ among the layers71, 72, 71, 72, and 71 of the multilayer film 7. If the high refractiveindex layer 71 and the low refractive index layer 72 have a largethicknesses, light propagating therein is absorbed by the layers andattenuated, so that a smaller N is preferable. Also, a film ofaggregated nano-particles of a large thickness tends to develop a defectsuch as a fracture, so that a single layer of a thickness exceeding 750nm is difficult to form. The thicknesses d₁ and d₂ of the highrefractive index layer 71 and the low refractive index layer 72 can beadjusted by the composition of each slurry and a coating amount per unitarea.

n ₁ ·d ₁=(2N−1)/4·λ  (1)

n ₁ ·d ₂=(2N−1)/4·λ  (2)

It is preferable that the multilayer film 7 efficiently reflects bluelight emitted by the light emitting element 1 and also transmits greenlight and red light that are wavelength converted by the fluorescentmaterials 61 and 62 with higher intensity. For example, changing thevalue N in the formulas (1) and (2) to adjust the film thicknesses d₁and d₂ of the high refractive index layer 71 and the low refractiveindex layer 72 so that the product (optical film thicknesses) of therefractive indices n₁ and n₂ at the peak wavelength λ′ of the greenlight or the red light and the thicknesses d₁ and d₂ respectivelysatisfy the relationships shown in the formulas (3) and (4) below. Thus,the intensity of the reflected light of the wavelength λ′ can beminimized. In some cases, satisfying the formulas (1) and (3), and alsothe formulas (3) and (4) may be difficult, and further, satisfying thoseformulas with both the light emitted from the two types of thefluorescent materials 61 and 62 may not be practical. For this reason,simulation is preferably used to design the film thicknesses d₁ and d₂,and the number of the pairs of the high refractive index layer 71 andthe low refractive index layer 72 so that desired reflectances can beobtained at the three wavelengths of light: blue light from the lightemitting element 1 and green light and red light from the fluorescentmaterials 61 and 62. The multilayer film 7 having such a structuredescribed above allows passing of much light whose wavelength isconverted by the fluorescent materials 61 and 62, in addition tostrongly reflecting blue light emitted from the light emitting element1. Accordingly, the wavelength conversion efficiency can be furtherimproved, which allows a reduction in the content amount of thefluorescent materials 61 and 62, while enhancing the light extractionefficiency of the light emitting device 10.

n ₁ ′·d ₁ =N/2·λ′  (3)

n ₂ ′·d ₂ =N/2·λ′  (4)

The wavelength “λ” in the formulas (1) and (2) and simulation is ideallya measured value of the peak wavelength of light emitted by the lightemitting element 1 mounted in the light emitting device 10, but may beapproximated by a designed value λ₀ of the peak wavelength of lightemitted by the light emitting element 1. Similarly, the wavelength “λ′”is ideally a measured value of the peak wavelength of light emitted byeither the fluorescent material 61 or 62 in the light emitting device10, but may be approximated by a designed value of the peak wavelengthof light emitted by either the fluorescent material 61 or 62. Themeasured values of those wavelengths can be obtained by measuring duringmanufacturing the light emitting device 10, as described further below.Meanwhile, the high refractive index layer 71 and the low refractiveindex layer 72 constituting the multilayer film 7 may each includes acertain degree of in-plane unevenness in the film thickness, and furtherin the refractive index due to the particle size, the state ofaggregation (filling rate), etc., of the nano-particles 71 a and 72 a.The multilayer film 7 in which the high refractive index layers 71 andthe low refractive index layers 72 as described above are layered tendsto have a reflectance to the light of the wavelength λ smaller than thatof the designed value, so that the number of pairs is preferablydesigned by measuring the reflectance of the samples, rather than by asimulation. The degree of in-plane unevenness in the thickness and therefractive index of the high refractive index layer 71 and the lowrefractive index layer 72 can be controlled by the particle size of theprimary particles in the slurry, the type and content of the solvent anddispersion agent, coating condition, coating amount, and so force, ofthe respective layers and the degree of about several percent or less toabout one percent or less is preferable.

Accordingly, a light emitting device according to other certainembodiments may have a configuration as shown below. A light emittingdevice includes a light emitting element, a light-transmissive membercovering the light emitting element and configured to allow light fromthe light emitting element to pass through, a fluorescent materialcontained in the light-transmissive member to convert wavelength oflight from the light emitting element, and a multilayer film disposed onthe light-transmissive member. When the peak wavelength of light emittedfrom the light emitting element is indicated as λ, at least one film inthe multilayer film satisfies n₁·d₁=(2N−1)/4·λ (where d₁ is thethickness of the film, n₁ is the refractive index at the peakwavelength, and N is a natural number), and at least one film in themultilayer film satisfies n₂·d₂=(2N−1)/4·λ (where d₂ is the thickness ofthe film, n₂ is the refractive index at the peak wavelength, and N is anatural number which is n₂≠n₁). The multilayer film in the lightemitting device contains the films having the thicknesses in the rangesshown above. Thus, reflection of the blue light emitted from the lightemitting element can be enhanced, allowing an increase of absorption ofthe blue light in each of the fluorescent materials, which in turn canincrease the intensities of the green light emission and the red lightemission of the light emitting device. Accordingly, emission from thelight emitting element in the green region can be reduced relatively.

Also, a light emitting device according to other certain embodiments mayhave a configuration as shown below. A light emitting device includes alight emitting element, a light-transmissive member covering the lightemitting element and configured to allow light from the light emittingelement to pass through, a fluorescent material contained in thelight-transmissive member to convert wavelength of light from the lightemitting element, and a multilayer film disposed on thelight-transmissive member. When the peak wavelength of light emittedfrom the light emitting element is indicated as λ′, at least one film inthe multilayer film satisfies n₁′·d₁′=N/2·λ′ (where d₁′ is the thicknessof the film, n₁′ is the refractive index at the peak wavelength, and Nis a natural number), and at least one film in the multilayer filmsatisfies n₂′·d₂′=N/2·′ (where d₂′ is the thickness of the film, n₂′ isthe refractive index at the peak wavelength, and N is a natural numberwhich is n₂′≠n₁′). The multilayer film in the light emitting devicecontains the films having the thicknesses in the ranges shown above.Thus, reflection of the green light and red light emitted from thefluorescent materials can be reduced, which in turn can increase theintensities of the green light emission and the red light emission ofthe light emitting device. Thus, optical intensity in a region betweenblue color and green color can be reduced.

The light emitting device according to those other certain embodimentspreferably has the multilayer film of dielectric multilayer film.

Operation of Light Emitting Device

Operation of the light emitting device according to one embodiment willbe described with reference to FIG. 1 and FIG. 3. FIG. 3 is a schematicpartial cross-sectional view of the light emitting device, schematicallyillustrating operation of the light emitting device according to oneembodiment. In operation of the light emitting device 10, electriccurrent is supplied to the light emitting element 1 from an externalpower source through the leads 3 a and 3 c and the wires 4, to cause thelight emitting element 1 to emit light. Blue light L_(B) emitted fromthe light emitting element 1 propagates in the light-transmissive member5. While propagating, a portion of the blue light L_(B) hits thefluorescent material 61 or the fluorescent material 62 dispersed in thelight-transmissive member 5 and is converted to green light L_(G) or RedLight L_(R). Light from the light emitting element 1 directly or bypropagating through the light-transmissive member 5 reaching thesurfaces defining the recess of the light-transmissive member 2 or theinner lead portions of the leads 3 a and 3 b at the bottom surface ofthe recess is reflected back into the light emitting element 1 or thelight-transmissive member 5 and propagates again. The blue light L_(B),green light L_(G), and red light L_(R) that have leached the multilayerfilm 7 from the upper surface of the light-transmissive member 5 passthrough the multilayer film 7 and mixed, and then extracted to theoutside of the light emitting device 10 as a white light. At this time,a portion of light, particularly a portion of the blue light L_(B) isstrongly reflected by the multilayer film 7 and returns to thelight-transmissive member 5. The light returned in thelight-transmissive member 5 propagates again in the light-transmissivemember 5, and while propagating, blue light L_(B) that hits thefluorescent materials 61 and 62 is converted to green light L_(G) or redlight L_(R). A portion of the converted light may be reflected at thesurfaces etc., of the recess of the light-reflecting member 2 and aportion of the converted light passes through the multilayer film 7 andextracted to the outside of the light emitting device 10.

As described above, in the light emitting device 10, repetitivepropagation of much of the blue light L_(B) caused by the multilayerfilm 7 increases the blue light L_(B) hitting the fluorescent materials61 and 62, so that the wavelength conversion efficiency can beincreased. Therefore, the higher the reflectance of the blue light LB,that is light of peak wavelength λ, the greater red component(chromaticity coordinate x) and green component (chromaticity coordinatey) in the light, with respect to the blue light, extracted to theoutside of the light emitting device 10. Further, the higher thetransmittance of the green light L_(G) and the red light L_(R) of themultilayer film 7, the further greater red component and green componentin the extracted light. In other words, adjusting the reflectance forlight of a wavelength λ or further, adjusting transmittance of light ofa wavelength λ′ of the multilayer film 7 allows for adjusting a shift ofchromaticity from the light before reaching the multilayer film 7 to thelight extracted to the outside of the light emitting device 10, so thatthe color of the extracted light can be adjusted to a desired color.

The chromaticity coordinates x, y are used for indication of colorcharacteristic of light, and for example, numerical values based on achromaticity diagram of the XYZ colorimetric system as defined by theInternational Commission on Illumination (CIE). The chromaticity can bemeasured by using a commercially available chromoscope. In other words,in the light emitting device 10, even when the colors of light reachingthe multilayer film 7 fluctuate, the multilayer film 7 is designed toreflect light of the wavelength λ at a predetermined reflectance, basedon the color of light, so that the fluctuation in the color of light canbe corrected. The shifting amount in the chromaticity of light by themultilayer film 7 can be designed based on measuring the chromaticity oflight before disposing the multilayer film 7 in the manufacturing of thelight emitting device 10, as in the method of manufacturing describedbelow.

Operating Display Device

Next, a display device using a combination of the light emitting deviceaccording to the present embodiment and a color filter will bedescribed. FIG. 4 is a schematic diagram showing matching between theemission spectrum of the light emitting device according to oneembodiment and transmission spectra of three different color filters.FIG. 5 shows chromaticity coordinates of light from the light emittingdevice according to one embodiment and light from the light emittingelement and the fluorescent material in the light emitting devicetransmitted through the color filters.

The display device includes a lighting device having the light emittingdevice described above, and a display panel provided with a color filterhaving a plurality of color portions at least including portions havinga blue color, a green color, and a red color, and configured to displayan image by using light from the lighting device. More specific examplesof the display device include liquid crystal display devices. Thelighting device can be a backlight in which the light emitting devicemay be singly used or a combination of a light guide plate and the lightemitting device may be used. Liquid crystal is used for the displaypanel and a color filter is provided on the display panel. The displaydevice can produce the effects described below.

The liquid crystal display device includes a backlight having the lightemitting device 10 and a light guide plate, and a liquid crystal displaypanel and a color filter are arranged at the light-extraction side ofthe backlight. The color filter includes a color portion at leastincluding portions having a blue color, a green color, and a red color.A backlight can improve, with provision of a color filter, the purity ofred light and green light transmitted through the color filter, allowingfor expansion of the color reproduction range of a liquid crystaldisplay device incorporating the backlight. That is, with provision ofthe multilayer film 7, the emission peak in blue region slightlydecreases but the emission peaks in green region and red region increasein the light emitting device 10. Generally, in the liquid crystaldisplay devices, a green region in the color filters also transmits aportion of short wavelength component of blue light from a lightemitting element and a portion of long wavelength component of red lightfrom a red fluorescent material as well as green light from a greenfluorescent material. Consequently, the color purity of the green lightdecreases. Whereas, the light emitting device described above has amultilayer film that provides higher intensity of green light relativeto blue light and red light in green region, compared to that does nothave the multilayer film, which is considered attributable to theimprovement in the green color purity. The same is considered in theimprovement in the red color purity in red region. Thus, with the use ofthe light emitting device 10 as the backlight, in combination with adisplay panel provided with a color filter, a display device that canemit light of deep green and/or deep red can be obtained. Accordingly, adisplay device having a wider color reproduction range can be provided.

Method of Manufacturing Light Emitting Device

Next, a method of manufacturing the light emitting device according tocertain embodiments will be described with reference to FIG. 6. FIG. 6is a flow chart showing a flow of a method of manufacturing a lightemitting device according to one embodiment. The method of manufacturinga light emitting device includes providing a light emitting device(S10), in which a light emitting device having a light emitting elementdisposed on a light-reflecting member and the light emitting element iscovered by a light-transmissive member containing a fluorescentmaterial, and disposing a multilayer film (S30), in which a multilayerfilm is disposed. In the step of providing the light emitting device(S10), providing a light emitting element (S11) in which a lightemitting element is provided, providing a package (S12), in which alight-reflecting member combined with leads is formed to obtain apackage, then, mounting the light emitting element (S13) in which thelight emitting element is mounted on the package, and disposing alight-transmissive member (S14), in which a light-transmissive member isdisposed, are performed in sequence. The step of providing the lightemitting element (S11) and the step of providing the package (S12) areperformed independently of each other, and may be performed in anappropriate order, or simultaneously. Further, measuring chromaticity(S20) in which the light emitting element is caused to emit light andthe chromaticity of light transmitted through the light-transmissivemember is measured may be performed before the step of disposing themultilayer film (S30), to obtain the light emitting device.

Providing Light Emitting Element

In the step of providing the light emitting element (S11), the lightemitting element 1 is provided. For example, a nitride-basedsemiconductor is grown on a substrate made of sapphire or the like,where an n-type semiconductor layer, an active layer (light emittinglayer), and a p-type semiconductor layer are layered in order. Then, ateach predetermined portions, the p-type semiconductor layer and theactive layer are removed to expose corresponding portion of the n-typesemiconductor layer, and electrodes electrically connecting to the uppersurfaces of the n-type semiconductor layer and the p-type semiconductorlayer are respectively disposed. Then, the light emitting elements 1arranged in a matrix on a single substrate are singulated.

Providing Package

In the step of providing the package (S12), the package 20 is provided.A Cu-plate of a predetermined thickness is provided and punching or thelike is applied to form shapes of the leads 3 a and 3 c, then Ag platingis applied to obtain a lead frame having the leads 3 a and 3 c. Then,using a resin material containing a light-reflecting material, thelight-reflecting member 2 with interposing leads 3 a and 3 c is formedby way of injection molding or the like, to obtain the package 20.

Mounting Light Emitting Element

In the step of mounting the light emitting element (S13), a lightemitting element 1 is mounted on the package 20. The lower surface ofthe light emitting element 1 is fixed via an adhesive or the like, onthe lead 3 a at the bottom surface of the recess of the light-reflectingmember 2. Subsequently, wire-bonding is performed to electricallyconnect the electrodes of the light emitting element 1 and the innerlead portions of the leads 3 a and 3 c with the wires 4, respectively.

Disposing Light Transmissive Member

In the step of disposing the light-transmissive member (S14), thelight-transmissive member 5 is disposed. Using a dispenser or the like,a predetermined amount of a resin material containing the fluorescentmaterials 61 and 62 is applied in drops in the recess of thelight-reflecting member 2. Then, a processing appropriate to the resinmaterial, such as heating is performed to harden the resin material inthe recess to obtain the light-transmissive member 5 containing thefluorescent materials 61 and 62.

Measuring Chromaticity

In the step of measuring chromaticity (S20), a power source is connectedto the outer lead portions of the leads 3 a and 3 c to supply electriccurrent to the light emitting element 1 to cause emission and thechromaticity of light transmitted through the light-transmissive member5 is measured. From the measured x-value and y-value of the chromaticityof the light, the shift amounts Δx and Δy necessary for obtaining thedesired chromaticity for the completed light emitting device 10 arecalculated.

Disposing Multilayer Film

In the step of disposing the light-transmissive member (S30), amultilayer film 7 is disposed on the light-transmissive member 5. In thestep, slurries for the high refractive index layer 71 and the lowrefractive index layer 72 are respectively provided. Primary particlesof TiO₂ and SiO₂ are dispersed in a corresponding organic solvent suchas toluene, ethanol, or the like to obtain respective slurries. At thistime, the primary particles are preferably dispersed uniformly in therespective slurries. Thus, as needed, a pre-treatment such as a surfacetreatment on the primary particles or adding of ahigh-molecule-dispersing agent such as an acrylic-based dispersing agentin the slurry may be performed. Then, the obtained two types of theslurries are applied alternatively on the light-transmissive member 5.For applying the slurry, any appropriate method that allows adjustingthe coating amount per unit area can be used, and examples thereofinclude a potting method, an ink-jet method, a spray method, a spincoating method, and a dipping method. In the present embodiment, in aplan view, the sizes of the high refractive index layer 71 and the lowrefractive index layer 72 are in conformity to the shape of the recessof the light-reflecting member 2, so that appropriate sizes of thelayers can be obtained by adjusting the applying amount of the slurry,and in the present embodiment, a potting method is employed and adispenser or the like can be used as in the step of disposing thelight-transmissive member (S14).

An amount of the slurry for the high refractive index layer 71 to obtaina thickness d₁ after dried is applied in drops so as to spread on theentire of the light-transmissive member 5 in the recess of thelight-transmissive member 2. When the slurry on the light-transmissivemember 5 is dried, the primary particles of TiO₂ are aggregated whilethe organic solvent is evaporated, to give a film of aggregatednano-particles of TiO₂. At this time, a drying method such as naturaldrying, warm air drying, oven drying, or the like may be used. Thedrying time can be determined according to the drying method, thecontent and dropping amount of the slurry, and drying time of at leastone second to several tens of seconds may be employed so that the slurrywill not mix with the slurry applied thereon and not cause a decrease inproductivity. Next, in a similar manner, an amount of the slurry for thelow refractive index layer 72 to obtain a thickness d₂ after dried isapplied in drops. Similar operations are repeated and after applyingdrops for the uppermost layer of the high refractive index layer 71, allthe five layers are completely dried by using an oven, blowing warmwind, or by drying naturally to obtain the multilayer film 7.

The multilayer film 7 is preferably designed by determining thereflectance to light of the wavelength λ and the transmittance of lightof the wavelength λ′ based on the shift amount Δx and Δy of the color oflight calculated in the step of measuring chromaticity (S20), anddetermining the number of the pairs and the film thicknesses d₁ and d₂of the high refractive index layer 71 and the low refractive index layer72. For example, when the x-value and the y-value of the chromaticity ofthe measured light are smaller than the reference values, the number ofthe pairs is increased to increase the shift amount of the chromaticitycaused by the multilayer film 7. That is, for each of the light emittingdevices 10, the thicknesses d₁ and d₂ of the high refractive index layer71 and the low refractive index layer 72 can be set according to thechromaticity of the light measured in the step of measuring thechromaticity (S20), and the dropping amount of the slurry and the numberof layers can be determined.

Further, the film thickness d₁ and d₂ of the high refractive index layer71 and the low refractive index layer 72 may be designed based on themeasured values of the peak wavelength λ of light emitted by the lightemitting element 1 and the peak wavelengths λ′ of light emitted from thefluorescent materials 61 and 62.

For example, in the step of measuring chromaticity (S20), the emissionintensity is also measured in addition to the chromaticity of the lightto obtain the peak wavelengths λ and λ′. Alternatively, in the step ofproviding the light emitting element (S11), before or after singulatingthe light emitting element 1, or after the step of mounting the lightemitting element (S13), the light emitting element 1 may be caused toemit light to measure the peak wavelength λ of the light.

In the method of manufacturing the light emitting device according tothe present embodiment, the film thickness and the number of therespective layers of the multilayer film can be easily changed for eachlight emitting device, and even when the wavelength of light emittedfrom the light emitting element and the content amount of thefluorescent materials fluctuate, light emitting devices that allowextraction of desired color of light can be obtained. Moreover, eachfilm of the multilayer film can be formed in the limited region bypotting or the like, so that provision of a mask or the like, becomesunnecessary.

As described above, the light emitting device according to the presentembodiment can emit substantially uniform light despite of unevenness inthe wavelength of light emitted from the light emitting element or inthe content of the fluorescent material, further, high wavelengthconverting efficiency of the fluorescent material and high lightextraction efficiency are realized, and can be manufactured with goodproductivity.

Variation

The multilayer film 7 may include one or more layers of the high or/andlow refractive index layers 71 and 72 adapted to cause Rayleighscattering of blue light emitted by the light emitting element 1, inthis case, this configuration is preferably applied to the lowermosthigh refractive index layer 71 and the particle size of thenano-particles 71 a is accordingly adjusted. The multilayer film 7 mayhave the low refractive index layer 72 as its lowermost layer, andparticularly when there is a large difference between the refractiveindex of the low refractive index layer 72 and the light-transmissivemember 5, a higher reflectance can be obtained. Further, the multilayerfilm 7 may have a low refractive index layer 72 as its uppermost layer,which reduces the difference in the refractive indices between the lightemitting device 10 and the ambient air, which in turn increases thetransmittance of light at the upper surface, so that the lightextraction efficiency can be increased.

In the light emitting device 10, the upper surface of thelight-transmissive member 5 may be arranged approximately co-planar tothe upper surface (edge of the upper surface defining the opening of therecess) of the light-reflecting member 2 and the multilayer film 7 maybe disposed on the upper surface of the light-transmissive member 5 andthe upper surface of the light-reflecting member 2 that is locatedoutward of the light-transmissive member 5. In this configuration, theedge of the light-reflecting member 2 surrounding the opening of therecess of the light-reflecting member 2 is covered by the multilayerfilm 7 and the strength of the opening edge can be improved.Alternatively, the light emitting device 10 may have the multilayer film7 disposed so that a portion of the light-transmissive member 5 isexposed, with this, the color of the extracted light can be adjusted bythe exposed area of the light-transmissive member 5.

EXAMPLES

The examples will be described below. FIG. 7 is a diagram showing asimulation result of a reflection spectrum of five-layer film ofTiO₂/SiO₂, and an emission spectrum of light from the light emittingelement and the fluorescent material of the light emitting device. FIG.8 is a diagram showing ratios of the emission intensities of the lightemitting device after disposing a three-layer film or a five-layer filmto before disposing respective layered film, in which films ofaggregated TiO₂ nano-particles and aggregated SiO₂ nano-particles arealternately layered. In Examples, samples of the light emitting deviceshaving a three-layer film or a five-layer film of the multilayer filmare provided. In each sample, emission spectrum and chromaticity oflight extracted before disposing the multilayer film are measured, andthe change in the emission intensity and chromaticity due to themultilayer film

The three-layer film has a structure of TiO₂/SiO₂/TiO₂ and thefive-layer film has a structure of TiO₂/SiO₂/TiO₂/SiO₂/TiO₂,respectively layered in order. In order to obtain a high reflectance toblue light and approximately 0% of reflectances to green light and redlight, the film thicknesses were determined by simulation, and athickness of 90 nm for a TiO₂ film and a thickness of 130 nm for a SiO₂film were designed. In the simulation, the refractive indices of TiO₂film and the SiO₂ film are 2.70 and 1.46, respectively, thelight-transmissive member under the multilayer film is silicone with therefractive index of 1.53, and the refractive index of the ambient air is1.0, and no-change in the wavelength is assumed, and a reflectionspectrum was obtained.

In each of the light emitting device samples, an LED configured to emitlight of 450 nm was used as the light emitting element. The lightemitting element was mounted in a package for a side-view type lightemitting device, then, a light-transmissive silicone resin having afluorescent material contained therein was applied to seal the lightemitting element, and a light-transmissive member was formed. For thefluorescent material, two types of fluorescent materials:Si_(6-z)Al_(z)O_(z)N_(8-z):Eu (β-sialon-based fluorescent material) forgreen light (peak wavelength 540 nm) and K₂SiF₆:Mn (KSF fluorescentmaterial) for red light (peak wavelength 630 nm) were used. In thisstate where the light-transmissive member was formed, electric currentwas supplied to the light emitting element to cause the light emittingelement to emit light, and the emission spectrum and the chromaticitywere measured. Further, the multilayer film was disposed on thelight-transmissive member, as described below, to obtain a sample of thelight emitting device.

Slurry to form the TiO₂ film and the SiO₂ film were preparedrespectively. Toluene was used as the solvent and 0.5 wt % of TiO₂particles of average particle size 30 nm together with 0.2 wt % of adispersion agent were dispersed in toluene. Ethanol was used as thesolvent and 0.5 wt % of SiO₂ particles of average particle size 25 nmtogether with 0.2 wt % of a dispersion agent were dispersed in ethanol.The slurry dispersed with TiO₂ particles was discharged on thelight-transmissive member from a nozzle of 100 μm diameter of a jetdispenser, at 0.7 mm intervals with an amount calculated based on theparticle concentration to obtain a thickness of 90 nm. Then, the slurrywas left stand for about 10 seconds to be naturally dried to form a filmof aggregated TiO₂ nano-particles on the light-transmissive member. Onthe obtained film, the slurry dispersed with SiO₂ particles was appliedin a same manner as described above, with a calculated amount to obtaina thickness of 130 nm, then, naturally dried to form a film ofaggregated SiO₂ nano-particles. Those operations were alternatelyrepeated to dispose three-layer film (TiO₂/SiO₂/TiO₂) or five-layer film(TiO₂/SiO₂/TiO₂i O₂/SiO₂/TiO₂) of TiO₂ and SiO₂, then dried in an ovenat 110° C., for 120 minutes to form the multilayer film, thus obtainedthe samples of the light emitting devices. Also, as reference examples,samples of light emitting devices having a single layer of SiO₂ film ora TiO₂ film on the light-transmissive member were formed.

The light emitting element in each of the obtained samples was caused toemit light and the emission spectrum and chromaticity were measured. Theratios of the emission intensities at different wavelengths and theshift in chromaticity respectively to those before disposing themultilayer film were calculated. The ratios of the change in theemission intensities are shown with respect to 100% when no changeoccurred.

TABLE 1 Change in Emission Change in Color Intensity, % ReproductionShift in Chromaticity Film Structure 450 nm 540 nm 630 nm Range, % Δx ΔySiO₂ 102.06 100.60 99.94 99.9 −0.0028 −0.0034 TiO₂ 93.77 100.08 99.94100.4 +0.0045 +0.0084 TiO₂/SiO₂/TiO₂ 94.20 101.10 101.35 100.5 +0.0054+0.0096 TiO₂/SiO₂/TiO₂/SiO₂/TiO₂ 83.92 102.32 103.50 101.3 +0.0140+0.0249

With the multilayer film, the light emitting devices each exhibited adecrease in the emission intensity near the wavelength of 450 nm, and anincrease in the emission intensity in two wavelength ranges near 540 nmand near 630 nm, and further, the greater the number of the layeredfilms, the greater the ratios of the change. As a result, thechromaticity coordinates x, y of the light showed sifts to + directions,and further, greater shifts were confirmed with the five-layer film. Thewavelength range where the emission intensity decreases with themultilayer film approximately conforms to the maximal value of thereflection spectrum of the five-layer film obtained by simulation. Insimulation, the reflectance changes in a crest shape with a peak at 410nm, whereas in the samples, either with the three-layer film or thefive-layer film, the emission intensity exhibited a decrease in anapproximately flat shape in a wide wavelength range of 420 nm to 480 nm.The sample with a TiO₂ single-layer film also exhibited a reduction inthe emission intensity in the wavelength range of 420 nm to 480 nm. Thisis thought to be due to a certain degree of in-plane unevenness in thethickness that each of the films of the aggregated nano-particles ofTiO₂ or SiO₂ may have. The difference of those with the high reflectancewavelength range obtained by the simulation is assumed due to error inthe thickness of the samples. Moreover, the decrease in the emissionintensity near the wavelength of 450 nm whereas the increase in theemission intensity near the wavelength of 540 nm and near the wavelengthof the 630 nm indicate that the multilayer film strongly reflects bluelight near the wavelength of 450 nm and that improve the wavelengthconversion efficiency of the fluorescent material. Further, the resultindicates that the multilayer film has a high transmittance to thewavelength range of light from the fluorescent material, whichapproximately agrees with the minimum value of the reflection spectrumof the five-layer film obtained by the simulation.

On the other hand, the light emitting device provided with the TiO₂single film exhibited approximately no change in the emission intensitynear the wavelength of 450 nm and near the wavelength of 630 nm. This isassumed that despite of an improvement in the wavelength conversionefficiency by high reflectance of blue light, the TiO₂ single film alsoreflects the wavelength-converted green light and red light and thatoffset the effects. Thus, the shift in the chromaticity of the light wassmaller than that of the light emitting device provided with thethree-layer film. Meanwhile, the light emitting device provided with theSiO₂ single film exhibited a shift in the chromaticity of the light inone direction. This is because the SiO₂ single film has a refractiveindex smaller than that of the silicone of the light-transmissive memberunder it and also the difference in the refractive indices is smaller,and thus the transmittance of the blue light is increased. Moreover, thearea of color reproduction range can be increased with a three-layerfilm and a five-layer film compared to that obtained with the SiO₂single-layer film. This is due to an expansion of the color reproductionrange of green and red.

As described above, the multilayer film of layered film of aggregatednano-particles was confirmed to cause shift in chromaticity of lightwith either three-layer film or five-layer film, where the five-layerfilm exhibited greater shift. Further, with those films, a stable,higher reflectance was confirmed in a wide wavelength range.

As shown in the above, a light emitting device and a method ofmanufacturing the light emitting device are illustrated in accordancewith the embodiments for carrying out the present invention, but thescope of the invention is not limited to the above description, andshould be widely understood based on the scope of claim for patent.Further, based on the above description, it will be obvious that variouschanges and modifications can be made therein without departing from thescope of the invention.

The light emitting device according to the embodiments of the presentdisclosure can be used as a light emitting device that can employvarious types of light emitting elements including a semiconductor lightemitting element such as a light emitting diode as its light source. Itis to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

What is claimed is:
 1. A method of manufacturing a light emitting devicecomprising: providing a light emitting device, the light emitting devicecomprising a light emitting element covered by a light-transmissivemember that is configured to allow light from the light emitting elementto pass through, and a fluorescent material to convert wavelength oflight from the light emitting element, the fluorescent material beingcontained in the light-transmissive member; and disposing a multilayerfilm on the light-transmissive member, comprising; applying a firstslurry comprising first nano-particles dispersed in a first solvent onthe light-transmissive member to dispose a first film of aggregatedfirst nano-particles; applying a second slurry comprising secondnano-particles dispersed in a second solvent on the first film todispose a second film, the second nano-particles having a refractiveindex different from a refractive index of the first nano-particles; andrepeating the disposing of the first film and the second film to disposea multilayer film having a predetermined number of layered films.
 2. Themethod of manufacturing a light emitting device according to claim 1,wherein in the step of disposing the multilayer film, after applying thefirst slurry, the first solvent is removed to form the first film. 3.The method of manufacturing a light emitting device according to claim1, wherein in the step of disposing the multilayer film, after applyingthe second slurry, the second solvent is removed to form the secondfilm.
 4. The method of manufacturing a light emitting device accordingto claim 1 further comprising: before the step of disposing themultilayer film, causing the light emitting element to emit light andmeasuring chromaticity of the emitted light; and in the step ofdisposing the multilayer film, determining a number of the first filmsand the second films to be layered or determining a thickness of atleast one film of the first films and the second films, based on thechromaticity.
 5. The method of manufacturing a light emitting deviceaccording to claim 1, wherein in the step of disposing the multilayerfilm, the first slurry and the second slurry are applied by using apotting method.
 6. The method of manufacturing a light emitting deviceaccording to claim 1, wherein the first film and the second film of themultilayer film each have a thickness of 750 nm or less.
 7. The methodof manufacturing a light emitting device according to claim 1, whereinthe first nano-particles of the first film and the second nano-particlesof the second film have particle sizes from 5 nm to 100 nm inclusive. 8.The method of manufacturing a light emitting device according to claim1, wherein a volume ratio of the first nano-particles relative to thefirst film is 50% or more.
 9. The method of manufacturing a lightemitting device according to claim 1, wherein a volume ratio of thesecond nano-particles relative to the second film is 50% or more. 10.The method of manufacturing a light emitting device according to claim1, wherein a refractive index of the first film is greater than arefractive index of the second film at a peak wavelength of lightemitted from the light emitting element.
 11. The method of manufacturinga light emitting device according to claim 1, wherein the multilayerfilm has the first film as its uppermost layer.
 12. The method ofmanufacturing a light emitting device according to claim 1, wherein thefirst film of the multilayer film is disposed adjacent to thelight-transmissive member and the second film is disposed on the firstfilm.
 13. The method of manufacturing a light emitting device accordingto claim 1, wherein the first nano-particles are TiO₂ and the secondnano-particles are SiO₂.